1. Field of the Invention
Ammonia (NH3) is a commonly used chemical prevalent in many industrial processes throughout the world. Ammonia may also be naturally occurring and is familiar to most of us as a mild irritant in small doses. In large concentrations, ammonia can be quite hazardous and, accordingly, ventilation and other safety precautions must be undertaken when working near ammonia. At normal temperatures and pressures, ammonia is a colorless gas made up of one part nitrogen to three parts hydrogen. Ammonia is lighter than air and has a sharp, pungent odor that serves as a warning of its presence. Although ammonia is a toxic gas, it is not a cumulative poison. Accordingly, removal from the source serves as the best protection. Ammonia is highly soluble in water and forms a solution known as ammonium hydroxide (NH4OH) or aqua ammonia which is commonly used as a household cleanser.
One industrial application that has historically made liberal use of ammonia is commercial and industrial refrigeration systems. For such a refrigeration system, anhydrous ammonia is typically used. Anhydrous ammonia is the liquid form of pure ammonia gas, and is technically water-free. Most refrigeration experts consider industrial grade anhydrous ammonia to be the most economical and efficient heat transfer medium for industrial refrigeration processes.
In an industrial refrigeration system, compressors, piping, and vessels containing anhydrous ammonia are generally prevalent throughout the plant. Such a refrigeration system will generally also feature lubricating oils which are inserted into the compressor to keep the compressor lubricated. Invariably, some of the oil or other lubricant will migrate throughout the system, mixing with the anhydrous ammonia to coat the piping system. Since the oil will serve as an insulator or retardant to heat transfer, a high prevalence of waste oil in a refrigeration system will compromise efficiency of the refrigeration process. In order to prevent deterioration of the refrigeration function, accumulations of waste lubricating oil will need to be purged from the system. Most commercial and industrial refrigeration units will include one or more ports located at a lower level in the piping system and arranged such that lubricating oil will accumulate there to be drained from the pipes for collection and/or discarding.
In the United States, the International Institute of Ammonia Refrigeration (IIAR) is generally recognized as the leading authority on issues related to the operation and maintenance of industrial refrigeration systems utilizing ammonia. The IIAR has set forth various publications detailing proper practices for the operation of ammonia refrigeration systems as well as safety guidelines. Among the most pertinent guides set forth, Bulletin No. R1 (1983) provides a comprehensive analysis of the use of anhydrous ammonia in a refrigeration system. The IIAR has also set forth specific oil draining guidelines which are to be used in removing waste oil from an ammonia refrigeration system. (See the August 1996 IIAR Oil Draining Guidelines.) The guidelines note that draining oil from an ammonia refrigeration system is a potentially dangerous process and should only be performed by properly trained personnel.
In order to remove used lubricating oil from an industrial refrigeration unit, the typical procedure employed is for an employee to use the refrigeration system pressure if it is positive, or otherwise raise the pressure to a positive value above atmospheric pressure. An OSHA-approved ammonia hose should be screwed into the oil drain valve port. The present inventor has found that this current method is greatly improved, if the drain line also includes a sight flow indicator such as, for example, Model 700 manufactured by Anderson Midwest. Such an indicator enables the employee performing the oil removal to see when all the oil is removed and liquid ammonia is passing the sight glass. At that point, the employee quickly closes the valve when it is discovered that all the oil has been drained.
A bucket is placed under the oil drain valve port before the valved is opened, and the oil will flow into the bucket for disposal. In the alternative, hand pumps or mechanical pumps may also be used. Even when a pump is used, the waste oil is still typically removed into a bucket or other open container for removal by an employee. Since the waste oil has been in contact with ammonia, invariably the waste material removed will be a mixture of oil with entrained ammonia.
Under the IIAR guidelines, recognition of the inherent safety risks of removal of the oil-ammonia mix requires that an employee proceed with goggles, gloves and face shield before opening the valve port. In addition, the personnel in charge should check the ventilation fan in the area where the oil is being drained and only perform oil removal when appropriate ventilation is available. As the mixture is released, ammonia will be noticed in the ambient air along with the undesirable environmental effects. The maintenance personnel should always be in a position on the up-draft side of the oil drain bucket for this reason. The IIAR guidelines also state that the personnel should remain in position at the oil pot and keep a vigilant watch during the draining process until such time as the valve has been properly repositioned. Of course, for the personnel involved, the foul smell of ammonia will be prevalent. Since many waste removal ports are located within proximity to other industrial systems or personnel stations, oil draining is sometimes not performed as regularly as it should be. Of course, this leads to the inevitable compromising of the refrigeration system efficiency.
What is needed in the art is a means by which the waste oil can be effectively separated from the ammonia and the ammonia neutralized such as to prevent the undesirable side effects associated with draining waste oil from a commercial refrigeration unit that utilizes ammonia.
2. Description of the Related Art
Since ammonia-based refrigeration systems are old in the art, patents related to the composition of such a system are long expired. Many old patents also disclose systems or mechanisms for removing lubricating oil from a refrigeration system. One of the older patents which is also typical of standard commercial refrigeration oil separation can be found in U.S. Pat. No. 1,836,318 by N. H. Gay. In that refrigeration system, the oil separator noted by numeral 26 in FIG. 1 is typical. Other patents of note include U.S. Pat. No. 3,304,697 by Ramsey wherein a centrifugal separator is disclosed for separating the gaseous and non-gaseous components of a fluid stream including a collection pump and dividing means. U.S. Pat. No. 3,304,741 by Weller also discloses an oil separation system for a refrigeration system wherein an oil separator is positioned at a lower level with respect to a refrigeration system, and comprises an oil sump for gravity flow of oil into the compartment. U.S. Pat. No. 3,438,218 by O'Neil features a standard oil separation system wherein separated oil may be returned to the system.
U.S. Pat. No. 5,407,355 by Sarritzu claims a process of recovery of ammonia from a liquid waste stream. The process consists of reacting the stream with pure carbon dioxide or a gaseous mixture rich in carbon dioxide and then reacting the resulting mix with calcium chloride such as to cause calcium carbonate to undergo thermal decomposition. The thermal decomposition step is carried out preferably not lower than 850° C. Accordingly, the system has little utility for use in connection with a commercial refrigeration system.
U.S. Pat. No. 5,001,908 by Mayer discloses an oil separator for a refrigeration system wherein oil is separated from vaporized refrigerant leaving the high pressure discharge side of the compressor. Mayer states that in the preferred embodiment, oil is removed from the incoming refrigerant vapor in two successive stages, a centrifugal stage and a coalescing filter stage. While novel in many respects, this system does not address how to deal with entrained ammonia prevalent in a waste lubricating oil in a refrigeration system.
The prior art also features an assortment of patents directed to oil recovery systems for centrifugal refrigeration equipment or chillers including U.S. Pat. No. 5,165,248 by Sishtla and U.S. Pat. No. 5,182,919 by Fujiwara.
Perhaps the closest prior art system found is U.S. Pat. No. 4,280,337 by Kemp. Kemp discloses a means for separating oil from an ammonia-based refrigerant for potential reuse. The Kemp system includes an improved oil separation tank having upper and lower zones connected to the bottom of a surge means. A first conduit is included for draining settled out oil from the bottom of the surge means into the oil separation tank while a second conduit conducts oil from the lower zone of the oil separation tank to the suction intake of the compressor. This is best illustrated in FIG. 1 of the patent. However, Kemp is directed essentially to oil recovery and does not address the problem of neutralizing ammonia for improved safety in the oil separation process.
U.S. Pat. No. 4,559,210 by Diemer et al. is a multi-stage washing operation for the removal of ammonia from a gas stream. The method includes the steps of washing out ammonia from gas with a liquid enriched with ammonia in an ammonia washer followed with a washing with ammonia-free water at a second wash stage. A partial stream of waste water is then divided from the remainder and the partial stream is treated by the addition of sulphuric acid before being reintroduced into the final wash stage.
U.S. Pat. No. 4,689,156 to Zibrida involves removing ammonia from waste water by treating the waste water with an alkaline reagent consisting of lime and caustics sufficient to raise the pH to a value of at least 12.4. At that point, the waste water is subjected to a gas stripping exercise, said stripping being controlled to maintain the free ammonia equivalents of the waste water to at least 12.4 and acidifying the stripped waste water to lower the unionized ammonia content to less than 0.05 ppm NH3(N).
The prior art also includes a number of patents directed to processes for removing ammonia from a waste stream that are tangentially relevant to the present invention. For example, U.S. Pat. No. 3,540,189 by Siewers et al. is directed to a process for removing ammonia which has been formed during the de-gasification of coal in a coke oven in order to prevent the gas pipes from becoming corroded and in order to avoid formation of oxides in the smoke. U.S. Pat. No. 4,410,503 by van Nassau et al. involves a process for removing urea, ammonia and carbon dioxide from an aqueous solution. The method involves feeding a urea containing process condensate, relatively poor in ammonia, into an upper portion of a reaction chamber where it is heated by means of steam fed into the bottom of the column. The temperature and pressure in the column is maintained such that urea is decomposed therein into ammonia and carbon dioxide. The steam serves not only as a heating agent, but also as a stripping agent.
U.S. Pat. No. 4,456,535 by Zuidam et al. is a process for removing urea, ammonia and carbon dioxide from an aqueous solution by hydrolysis of urea and desorption of the ammonia and carbon dioxide. The solution is passed into the top portion of a column at a pressure of between 10 and 30 bar and is caused to flow downward countercurrent to an upward gas stream. The patent states that the top of the reaction column should be maintained at a temperature of between 170° and 220° C. and the bottom of the column should be maintained at a temperature of between 180° and 230° C.
In general, a review of pre-existing methods and technology finds considerable prior art directed to both the creation and elimination of ammonia in specific circumstances. The prior art also shows numerous uses and arrangements of ammonia-based refrigeration systems. However, none of the prior art is directed to the issue of neutralizing entrained ammonia in a stream of waste lubricating oil leaving a commercial refrigeration system such as to eliminate the attendant safety risks associated with the task.